This invention relates to a color solid-state image sensor and, in particular, a double-layer type solidstate image sensor having a photoconductive film formed as an optoelectro-transducing area over a substrate.
A structure having a photoconductive film formed as an optoelectro-transducing area on a chip substrate is known in a color solid-state image sensor. The chip substrate is of a single-crystalline silicon type having a signal charge storing section and signal charge readout section. The stacking of the photoconductive film over the substrate permits a greater aperture ratio of the cell area, enhanced sensitivity and improved performance, such as the suppression of blooming.
A wiring pattern for transferring a signal, such as a clock signal, necessary for the operation of the solid state sensor is also formed on the surface of the substrate. The wiring pattern is formed on that surface portion of the substrate situated around the photoconductive film and has bonding pads to electrically connect the wiring pattern to an external circuit. It is necessary that the photoconductive layer be formed on only an initially allotted cell area of the substrate so as to prevent an overlap with the wiring pattern area. This is because the presence of any overlap between the photoconductive film and the wiring pattern area on the substrate prevents a bond from being made between the wiring pattern and an external wiring.
In order to provide a color solid-state image sensor it is further necessary to form a color filter layer on the surface of the resultant layer structure. The color filter layer is formed by diffusing a dye into organic matter, such as gelatin and milk casein. The color filter layer is spin-coated by a spinner on the top surface of the aforementioned layer structure. Since, however, that portion of the photoconductive film overlapping with the wiring pattern area on the substrate is removed prior to the spin coating of the color filter layer, the aforementioned layer structure to be coated with the color filter layer has an uneven top surface, with the result that a step corresponding to the thickness of the photoconductive film is formed between the light sensitive area and the wiring pattern. Therefore, the color filter layer is difficult to uniformly form due to the resultant uneven surface of the aforementioned layer structure. The surface nonuniformity of the color filter layer appears, for example, as a coating mark. In general, such an uneven coating tends to occur frequently at an edge portion of the photoconductive film having a planar surface corresponding to the light sensitive cell area on the substrate. That coating mark provides a cause for a smear (one kind of color noise) on a color reproduction image, thus degenerating a reproduction image quality greatly. As a result, a serious problem has been involved in a wider application of this invention to a "double-layer" type color solid-state image sensor.